Can't run scripts with user in /docker-entrypoint-initdb.d

[robertdecaire]

I've got a docker-compose file where I include the following:

services:
    postgres-12:
        image: postgres:12-alpine
        user: root
        volumes:
          - "${PWD}/init-script.sh:/docker-entrypoint-initdb.d/init-script.sh"

I'm expecting that is will run this script as root, but the very first line of the script is:

apk update

And this results in:

postgres-12_1        | ERROR: Unable to lock database: Permission denied
postgres-12_1        | ERROR: Failed to open apk database: Permission denied

I've seen this issue: #321 and it seems to suggest, along with the documentation on the image page, that I should be able to run scripts as the user I specify. However, it doesn't seem to be respecting this. I can run these commands without issue if I start the container without mounting the script and then ssh in to get a terminal prompt, but I want them to run automatically on first startup. The purpose is to download and install an extension via its makefile so that I don't have to manually install it every time I spin up a new db. So the script contains some apk commands to update and get dependencies (e.g. gcc) to install the extension.

[yosifkit]

Additionally, as of docker-library/postgres#253, these initialization scripts are run as the postgres user (or as the "semi-arbitrary user" specified with the --user flag to docker run;

- https://github.com/docker-library/docs/blob/3f614f38145dbf4f31cd3a99bd6f87a3c3c3487d/postgres/README.md#initialization-scripts

They cannot be run as root, as the entrypoint script steps down after initial db directory creation & permissions:

postgres/docker-entrypoint.sh

Lines 303 to 308 in 2f6878c

	# setup data directories and permissions (when run as root)
	docker_create_db_directories
	if [ "$(id -u)" = '0' ]; then
	# then restart script as postgres user
	exec gosu postgres "$BASH_SOURCE" "$@"
	fi

---

Edit: You should probably just be using a Dockerfile to create a custom image FROM postgres:[version] with the needed extension since starting a new container with an already initialized database will result in no extension.